Two Positional Isomers of Sialylheptasaccharides Isolated from the Urine of a Patient with Sialidosis

Abstract

We describe the structures of two positional isomers of sialylheptasaccharide isolated from the urine of a patient with sialidosis with partial deficiency of β-galactosidase. Based on structural studies including compositional sugar analysis, exoglycosidase digestion, chemical ionization mass spectrometry, proton nuclear magnetic resonance spectrometry, and methylation analysis, their structures were deduced to be as follows:
1. AcNeuα2→6Galβ1→4GlcNacβ1→2Manα1→3(Manα1→6)Manβ1→4GlcNac
2. AcNeuα2→6Galβ1→4GlcNacβ1→2Manα1→ 6(Manα1→3)Manβ1→4GlcNac
Sialyloligosaccharide 1 has previously been found in the urine and liver of patients with mucolipidosis I and II and sialidosis, but sialyloligosaccharide 2 has not been found yet in human urine. These two sialyloligosaccharides could not be completely separated by any chromatographic procedures tested. The analytical techniques, including methylation study and NMR spectroscopy, could not clearly detect the differences between them. However, α-mannosidase treatment gave important information for the structural analyses of these sialyloligosaccharides.